Constant moisture levels or wet / dry cycles?

This came up on another forum, and I thought it might be worthwhile to discuss this here also. Some believe that wet / dry cycles are advantageous. Others believe that constant optimal moisture is best. I'm in that second group.

I haven't seen hard data on this, but there is some anecdotal evidence that might shed some light. Many of us water with a constant drip system like Blumat. I'm not saying that every Blumat user is in 100% agreement, but the great majority feel that constant moisture is better. That was my experience also.

We know dry cycles cause microbes to go dormant. The way I see it, a dormant microbe isn't working.

Any thoughts?

I have thought about this as well... And this is why i have seriously considered trying some blumats.

I can't speak for all, but I was surprised at the difference. I had originally hooked up the Blumats for watering convenience, mostly.

I shoot for wet-damp cycles without ever going to full "dry". Truthfully though, "dry" is not actually dry at a microscopic level. There are three types of soil water.

-Gravitational water- Flows through soil (your runoff was gravitational water before it flowed out the bottom of your pot). Plants and microbiology can use this water.

-Capillary water - Water held in the soil by capillary pressure. This is the water that stays in the pot after you water. Plants and micro organisms can use this water.

-Hygroscopic water- This water is very strongly held to soil particles by surface forces. It cannot be removed from soil without applying heat. Plants cannot use this water (they will wilt even though the water is present). However, SOME microbiology CAN in fact survive with the help of this layer of "moisture".

I prefer to play it safe and water while there is still some capillary water present. If the pot still has a little heft to it, and you can feel ANY moisture with your finger, capillary water is still present.

hell yeah, go teaming with microbs

Yeah i think until i get blumats, ima let my soil dry out less before i water from here out. lol

Love that book....

Microbes don't go dormant in the time period you're implying, e.g. a matter of days. It takes somewhat extended periods of time for said dormancy, and even so what you call moist and what a microbe needs are very different things.

In my experience wet dry cycles are indeed advantageous, but I don't let the plant go full-on wilted. When I notice droop, I water, NOT before though. Every plant is different in what it wants, but cannabis is a plant that has evolved for literally tens of thousands of years on wet/dry cycles. It promotes root growth and maintenance, etc. I don't think you're going to find any evidence proving that one is diffiniteily better than another, indoor grow cycles are just too short, being less than 4 months. But keeping your medium constantly moist isn't a good thing, even with excellent airation you can have root problems, so it's not so much a matter of which is better, as which is more advisable. You're not going to yield less or cause your plant to suffer by cycling, but you can avoid lots of problems that "keep it moist" growers can't.

That's been my experience.

I've been wanting to get a blumat set-up, just kinda clueless on which ones to get. I use 1-3g smart pots which ones should I use?

B4THC4T- Welcome to the forums. You have a lot of excellent thoughts, obviously.

uromastyx- I'd use the smaller carrots and maybe 2 drippers.

Also, personally I would not share the same cautionary note regarding constant moisture. Certainly overly moist is always bad, but to clarify, I'm simply looking at the potential value of ranging between nicely moist - dry. I'm assuming we're not dipping into wet / anaerobic conditions.

Has anyone seen the extensive thread on IC? I don't recall any of the dozens of blumat users being any less than excited about the improvements, though I sure could have missed someone with a counter-experience. I would think it's the ability to dial it in for constant "moist" rarely "wet." Again, I would agree that too wet limits growth.

I have also found this to be medium dependent, same as described in articles. I measure the moisture levels with Tensiometers and have found that in my pots, ~10 kPa is optimal. When Spurr was looking into this he felt closer to 5 was good. As a baseline, you'd have to get close to 2-3 before you'd get runoff.

I also grow in Geopots which works well with this whole strategy.

Wet/dry cycles are for cactus, not cannabis. Keep it moist growing organic or not.

Just a curiosity sorta topic here. To each his own, but was curious what others thought is all.

I think medium plays a big role as well. I don't like to let peat dry out as much, because (for me, anyway) it tends to get a bit crusty and hydrophobic if it get too dry. Coco seems to wet a little easier, even if it gets crusty dry.

That said, both my current mixes are peat based with no coco.

Random thought, just for the sake of discussion (not necessarily my opinion one way or another)...

I wonder if the benefit of wet/drier cycle is that it hits that "perfect" moisture level for a short while each and every time you water. I know I see a little burst of growth after each time I water. The growth rate doesnt seem to be exactly steady; more like the growth rate fluctuates up and down with each watering, like a sine wave. The plants seem happy with it (I don't wait until they droop), and I can't complain, but it begs the question...

If you were able to dial in and maintain that "perfect" moisture level constantly, could you stay at the peak of that hypothetical sine wave?

I sure don't know...

What I do know is this cheese quake has temporarily turned me philsophical..

I think that's it exactly. My opinion also. Same as others with irrigation. When I dial in my drippers the soil is dry on top and just moist a couple inches down. Not wet ever. Anyway, that's just what I do. As long as you're watering, that's the bigger deal

Yup. I've thought a lot about the Blumats, but I'm not sure they are for me. I like playing around with different soil mixes, teas, top dressings, etc. Kindof a never ending experiment. I also like to mix up a bucket of whatever the plants look like they might need each time I check on them. If I were dialed in with a water only mix, the Blumats would be nice, but for now I'm sticking with the wet/damp deal...

How do you do top dressing if your soil stays dry on top? Just water it in while the Blumats are doing their thing?

I have a little well under each dripper where I add stuff. I also do a soil drench every so often.

Makes sense.

What do you mean you have a well under each dripper? At some point, i really want the blumats.

cacti only!! c'mon. so rainstorms and sunshine don't count as wet and dry cycles? the earth is perfectly and uniformly moist everywhere, all the time?
wet/ dry cycles are natural and beneficial imo.
dry cycles force the roots to search for water. living in the desert, I have noticed it in my gardens and shrubs/trees
I let them dry more between waterings in the veg cycle, but never in flower. learned the hard way


I grow in roots organics or a remixed version of, so I cant say about any other medium
I hand water, one solo cup at a time, until I see runoff
A local grower in the AZ section told me once that he gets faster growth by limiting water when he up-pots
I've doing this too and noticed better vigor in young plants.
he only gives them 1 solo cup of water instead of drenching the whole pot to get rid of dry spots and air pockets (I don't water for 2-3 days after up-potting nowadays)
I never realized the effect of over saturated soil.......ACTUALLY I wouldn't of said it was over saturated at all, I would've said it was perfect, cause I was conscious of over saturation!
but he showed me that I was using way more water than was necessary

I also don't drench my plants fully when I transplant. BUT, the soil I fill the new pot with is already a bit moist (I keep it that way while it's breaking down in a bin or trash can). I think having the soil a little dryer (moist, not wet/saturated) at transplant helps encourage the roots to explore their new territory. Also, this avoids the 1 week plus wait for the pot to dry to a point you can water it again. When it's dried to the point I can water again, I give a thorough, deep watering to prevent any dry/hydrophobic spots from forming in the new soil. By this time, there are some roots in the new soil, and it won't stay saturated for long.